Domed building construction and method



Feb. 17, 1970 Y J. F. BL'ASKI 3,495,365

DOMED BUILDING CONSTRUCTION AND METHOD Filed April 25, 1968 .4 Sheets-Sheet 1 I 3 man-N Feb. 17, 1970 J. F; BLASK. 3,495,365 DOMED buILDmG consmnuc'nou AND METBOD Y Sheets- Sheet Feb. 17, 1970 Filed April 25, 1968 J- F. BLASKI DOMED BUILDING CONSTRUCTION AND METHOD .4 Sheets-Sheet 5 jag Feb. 17, 1970 J. F. BLASKI DOMED BUILDING CONSTRUCTION AND METHOD File April 25, 1968 .4 Sheets-Sheet 4 United States Patent O US. Cl. 52-127 15 Claims ABSTRACT OF THE DISCLOSURE 'A domed building construction is disclosed including a method of construction and prefabricated components whereby a dome structure may be formed which is essentially self-supporting during the construction process. Elaborate supporting scaffolding or the like is thus eliminated. A prefabricated module is disclosed and comprises two doubly curved longitudinally tapered panels connected along a longitudinal edge to form a longitudinally arcuate, tapered, trough-like module having a generally V-shaped cross-section. Crossbars are connected between the unjoined longitudinal edges of the V-shaped modules for transverse stress bearing as part of the prefabricated module and further cross bars are connected between the joined longitudinal edges of adjoining modules also for transverse stress bearing. A plurality of such tapered modules are interconnected to form a dome, and a compression ring is disposed at the apex of the dome.

BACKGROUND OF THE INVENTION The field of the invention relates to building constructions and methods of fabrication. More particularly it relates to dome building constructions and fabrication methods whereby such domes may be quickly and easily fabricated at a low cost and it is an object of the invention to provide improved buildings and methods of this character. A basic precept and object of the invention is that of preconstructing uniquely shaped modules and interconnecting these modules, in an on going self-sup porting structure, at the construction site to form a domed building.

Typical prior art domed buildings have been partially formed of concrete poured on the site into forms fabricated for the purpose or by fabricating a metal skeleton of the dome followed by covering it with sheeting of some sort. In each of these cases, and others, it has been necessary to construct a scaffolding for supporting substantially all of the dome framework during the fabricating operations. Of necessity these have involved the expenditure of large amounts of time and manpower at the building site.

SUMMARY OF THE INVENTION It is, therefore, a principal object of the present invention to provide a domed building construction which may be quickly constructed with a minimum number of men and machines and with a minimum of supporting scaffolding or the like.

It is a further object to provide a domed building construction composed of uniquely shaped modules which comprise both the dome supporting structure and covering.

It is a further object of the invention to provide a domed building construction which is essentially structurally self-supporting as the construction proceeds.

One embodiment of a building constructed according to the present invention includes a plurality of longitudinally arcuate, tapered, trough-like modules having a generally V-shaped cross-section adapted to be joined together side-by-side to form an essentially annular self- Patented Feb. 17, 1970 p CC supporting ring, and end-to-end to form tapered arches, so that when the modules are connected both side-byside and end-to-end, and a compression ring is added at the apex, a dome is formed. a

Each of the modules described comprises two longitudinally and transversely curved metal panels each of which has a taper from one end to the other. Inner and outer flanges are attached to the longitudinal edges of the panel, and two panels are joined along corresponding inner flanges to form a longitudinally arcuate, tapered trough having a generally V-shaped cross-section. Tensile and compressive stress bearing rods, bars, or the like are aflixed at longitudinal intervals to the inner flanges of the unjoined edges of the panels. After the modules have been assembled in the annular ring, additional tensile and compressive stress rods, bars or the like are afiixed at longitudinal intervals to the joined edges of adjacent modules. If needed, the panels may be further stiffened in the longitudinal direction, by attaching angle members to the panels, as by welding from one end to the other.

In another embodiment of the invention, the longitudinally and transversely curved tapered panels may be stiffened by providing one or more integral longitudinal channels of arcuate cross-section on the panel surface.

Guide means are provided, in either case, to aid in aligning two modules in end-to-end relation during dome fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a domed building construction embodying the invention;

FIG. 2 is a plan view on a larger scale of a portion of the dome of FIG. 1, including the foundation support;

FIG. 3 is a broken sectional view taken substantially in the direction of arrows 33 of FIG. 2;

FIG. 4 is a broken plan view of a building construction module formed in accordance with the present invention;

FIG. 5 is a side elevational view of the building construction module of FIG. 4 taken in the direction of arrows 5-5 of FIG. 4;

FIG. 6 is an elevational view on a larger scale of one component of the building construction module and illustrating one step in assembling a building according to the invention;

FIG. 7 is a front elevational view on a larger scale taken in the direction of arrows 77 of FIG. 4, and including some additional structure;

FIG. 8 is a perspective view of a portion of the building construction module of FIG. 4;

FIG. 9 is a fragmentary sectional view on a larger scale taken substantially in the direction of arrows 99 of FIG. 4;

FIG. 10 is a fragmentary sectional view on a larger scale taken substantially in the direction of arrows 1010 of FIG. 4;

FIG. 11 is a fragmentary top view of the domed building of FIG. 1;

FIG. 12 is a sectional view on a larger scale taken substantially in the direction of the arrows 1212 of FIG. 11;

FIG. 13 is a sectional, elevational view of a dome being constructed in accordance with one form of the present invention;

FIG. 14 is a plan view of a second embodiment of a longitudinally and transversely curved panel forming part of the buiding construction module according to the invention;

FIG. 15 is a broken side elevational view on a larger scale of the panel of FIG. 14;

FIG. 16 is 'a sectional view on a larger scale taken substantially in the direction of the arrows 16-46 of FIG. 14; and

FIG. 17 is a fragmentary sectional view of a building according to the invention utilizing the panels of FIGS. 14-16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawings, the invention is shown embodied in dome 20 composed of a plurality of longitudinally arcuate, tapered, trough-like modules 21, having a generally V-sha-ped cross-section interconnected both longitudinally and transversely to form a dome surface element 21a. The apex of dome 20 is provided with a compression ring 22, to which the uppermost, tapered, longitudinal ends of the interconnected modules 2.1 are connected. The compression ring may comprise a circular, hollow member of generally rectangular cross-section, whose outer side is adapted to be engaged with the longitudinal ends of the modules 21 as by welding. It is understood that the compression ring may be composed of a plurality of arcuate hollow tube sections attached end-to-end.

The nature of the taper of the connected modules is illustrated in FIGS. 2 and 3 and is determined by the curvature of the particular dome configuration desired.

The domed structure disclosed herein may be thought of as a plurality of semi-arches or dome surface elements 21a composed of longitudinally connected modules 21, as shown in FIG. 3, the semi-arches being connected transversely in a circle to form the dome 20. The arches or dome surface elements 21a, while elements as such, are formed, as will become clear, by the formation of self supporting essentially annular rings of connected modules. The circumference of the dome base being larger than the circumference of the compression ring, the module structure, according to the invention, provides that the cross-section of each semi-arch be largest at its base and smallest at the compression ring connection, Accordingly, the modules which are connected end-to-end to form a semi-arch are tapered from one longitudinal end to the other, and the uppermost end of each module is equal in cross-section to the lowest end of the module connected above it. The dome shown in FIGS. 1, 2 and 13 may be a portion of a sphere but it will be realized any other configuration may be used, so long as the curvature of the panels and the taper of the modules conform to the dome configuration.

Referring now to FIGS. 4-10, the construction of the individual modules 21 is more clearly shown. Doubly curved panels 23 transversely tapered from one longitudinal end to the other are provided, each panel having inner flanges 23a, 23b and outer flanges 23c, 23d in contiguous angularly displaced relationship with each other.

The double curvature of the panel 23 comprises a longitudinal curvature and a simultaneous transverse curvature. The longitudinal curvature is the curvature in the plane of a panel 23, is that seen when a panel 23 is lying flat and it is related to the height of the dome. If a spherical type dome were being constructed the longitudinal curvature would be the radius of the sphere for one of the longitudinal edges. For the other edge the curvature would depend on dome dimensions, material strength and the like. This curve may be approximated in view as seen in FIG. although these are related by a function of the angle of the plate relative to the vertical. The transverse curvature is the curvature at right angles to the plane of a panel 23 and is the radius of curvature as viewed in the direction of arrow A in FIG. 7. This curvature is also related to the dome configuration and dimensions. The compound or double curvature of the panels is shown in perspective in FIG. 8. In copending applications of the same inventor,

Ser. Nos. 729,866 and 734,826 filed on Apr. 18, 1968 and Apr. 24, 1968, respectively, and each entitled Building Construction for different building constructions, doubly curved panels are also described. The panels in the copending applications are not tapered as in the panel herein disclosed, and are illustrated in connection with semi-cylindrical type buildings and not domes. The principles relating to doubly curved structural panels, as shown in the pending applications, may be used in connection with the panels of the subject invention.

Referring specifically to FIG. 7, inner flanges 23a and 2312 are shown attached along the longitudinal edges of panels 23 such as by Welding, for example, the inner flanges 23a and 23b having the same angularrelationship with the panel 23 but extending in opposite directions therefrom. Outer flanges 23c and 23d, welded, for example, as shown along one edge to flanges 23a and 23b, respectively, also have an identical angular relationship with the panel 23 and extend in opposite directions therefrom. The angularity of flanges 23a and 23b relative to the body of panel 23 is such that these flanges are vertical to the ground in the final panel position. The angularity of flanges 23 and 23d, while shown as being at right angles to the flanges 23a and 23b, may vary and may be less than ninety degrees so as to create a trough between these flanges of adjacent panels, if desired.

In constructing a module 21, two of the tapered, longitudinally and transversely curved panels 23 and attached flanges 23a, 23b, 23c and 23d are connected along a corresponding inner flange 23b, by welding, for example, as shown in FIG. 7, to form a longitudinally arcuate, tapered trough of generally V-shaped cross-section. Other attaching means besides welding may be used as understood by those skilled in the art.

In order to rigidify and strengthen the modules 21, and in order to allow them to bear horizontal stresses, transverse rods 24 (FIGS. 4, 7, 8 and 9) are provided along the upper edges of the module. These transverse rods 24 are connected, as by welding, to the unjoined inner flanges 23a, in a preliminary state of assembly, as shown at intervals along the length of the module. The transverse rods 24 may be made of hollow piping or solid bars, so long as they are capable of carrying the necessary tensile and compressive loads. Further, as shown in FIG. 7, after transverse connection of two modules 21, transverse rods 2411, or pipes, are also provided to be connected, as by welding, between the inner flanges 23b, which flanges were referred to above as being joined to form a longitudi-i nally arcuate, tapered trough of V-shaped cross-section. As a result, the completed dome will include a transverse system of rods 24 on the exterior of the dome connecting inner flanges 23a, and a second transverse system of rods 24a on the interior of the dome connecting inner flanges 23b.

In addition, in order to strengthen and rigidify the modules in the longitudinal direction, V-shaped stifi'eners 25 are provided to be attached longitudinally from end to end of the surfaces of panels 23 (FIGS. 5, 7 and 10). The supports or stiifeners 25 are preferably constructed of two strips of material joined along one edge, as by welding, to form a V and conform to the curvature of the panel 23 to which they are attached, as by welding also. While two stiffeners are shown attached to each panel, more or less may be used so long as economy of construction as well as strengthening and rigidifying of the modules is obtained.

A module 21 may be constructed by placing a flat, longitudinally tapered metal plate,-which has been cut or formed to the longitudinal curvature referred to, in a jig or fixture, arcuately bending it to the transverse curvature referred to and welding the flanges 23a-23d in place, while holding the pieces in the jig, if necessary. The curvatures of the panels are thus retained. The longitudinal stiffeners 25 are welded to the panel surfaces preferably after the jigs are removed. In the next step, two panels 23 are connected, as by welding, along inner flanges 23b (FIG. 7), and transverse support :rods 24 are welded be tween the inner flanges 23a thereby completing the module 21.

The described manner of forming the modules may be performed at the construction site itself, thereby eliminating significant transportation costs over constructing the modules at a factory and then shipping them to the site. Alternatively, the panels 23 could be curvedly formed in rolling machines at a factory. The flanges may be welded to the panel and two panels may be welded together, at the factory to form the longitudinally arcuate, tapered troughs of V-shaped cross-section. Thereafter, groups of attached panels nested together without the stress bars 24 may be shipped to the construction site.

Guide means 26 (FIG. 6) for guiding complementary panels ends into alignment with each other and holding them during module connection are attached to the top end of one panel 23 of each module 21. The guide means 26, as shown, include two metal arms 27 and 28 of unequal length, both bent at the same angle at a point the same distance from one end. Thus the ends of the unequal arms diverge to form a Y and include a slot 29 therebetween for easily receiving one end of the panel 23. The unequal arm length assists in the guiding function.

The guide means 26 are shown connected to the panels 23 by cooperating nuts and bolts 30 and 3012: during construction of the modules, but can be allowed to remain in place after construction is completed.

Utilizing modules as described, the dome 20 may be fabricated self-supportingly by constructing a series of annular rings of modules successively upon each other, each ring of modules including its own series of tensile and compressive stress rings. Thus, referring to FIGS. 2, 3 and 13, there are seen a first annular ring 31 of modules resting on a foundation 32, an annular ring 33 of modules disposed on ring 31 and so on until a final ring of modules 34 is disposed on the ring preceding it.

The foundation 32 (FIGS. 2 and 13) may be of any material suitable for supporting the dome 20, such for example, as reinforced concrete.

Interiorly of the base perimeter of the dome a scaffolding 35 is erected to be used in connection with the assembly of each annular ring of modules. Cranes 36 may be disposed upon the ground, or floor of the dome, or upon a scaffold 37. In FIG. 13, the scaffolds 35 and 37 are shown for a stage of construction well beyond the beginning, but it will be understood that similar scaffolds will be utilized near the outer perimeter of the dome at the beginning.

In carrying out the construction process according to one form the first module 21b of annular ring 31 is set into place on foundation 32 by a crane 36 and is held there by temporary scaffolding 33a and the crane, the module 21b being shorter than the regular length of module but otherwise being the same including the exterior stress bars 24. Next a regular length module 216, constructed as described, is set in place on foundation 32, alongside module 21b, and is held there by scaffolding 33a and the crane. The now adjoining flanges 23a of both modules 21b and 21c are welded together as along line 38 (FIG. 2) and the interior stress bars or rods 24a are welded to the flanges 23b of the adjoining modules 21b and 210 (the reference characters 21b and 210 also shown in FIG. 7 as exemplary of the construction process). Next another short module 21d, constructed as described, is set in place on foundation 32, alongside module 21c and is held there by scaffolding 33a and the crane. The now adjoining flanges 23a of both modules 216 and 21d are welded together as along line 39 (FIG. 2), and the interior stress bars or rods 240 are Welded to the flanges 23b of the adjoining modules 210 and 21d. In the same manner additional alternating long and short modules are put into place, welded together and the stress bars attached until the closed (annular) ring of modules at the base of the dome is completed. At this stage of construction the exterior stress bars 24 in effect form complete rings around the exterior of the assembled-modules and the interior stress bars in effect form complete rings around the interior of the assembled modules. Any tensile or compressive stresses developed in supporting the modules are taken by the stress rings and the ring of modules supports itself. The welding together of the adjoining flanges makes the structure, essentially, monolithic and thus provides additional support.

The Weight of modules above the base module ring is supported by the base ring modules and the outward forces are the greatest at the base ring of modules 31. Thus the width of panels 23 from longitudinal edge to longitudinal edge is the largest in modules of ring 31. Also the diameter of the rods, bars or pipes 24 and 24aconnecting the flanges 23a and 23b of the modules in ring 23 is subject to the largest tensile forces because the total effect of the weight of the modules above is exerted at the base. Thus the diameter of the stress bars may be larger at the base ring than for rings higher up. Since these stress bars and the width of the panels are such as to support the total weight of the dome and the stresses created thereby, the base ring of modules 31 will a fortiori support itself after the ring is completed and the temporary scaffolding 33a removed.

The second ring 33 of modules may now be added. The first module 21a of ring 33, by means of crane 36, is set into place with its lowermost part against and in registry with the uppermost part of module 21b and in between the projecting portion of module 210 on one side and the corresponding projecting portion of a module on the other side. The lower edge of panel 23 of module 21e is guided into registry by the guide fingers 27 and-28 on module 21b (as seen in FIG. 6). Temporary scaffolds 41a and 41b may be erected for use by workmen in attaching module 21e'and for additional support of this module. While the module 21e is being held in place its adjoining flanges 23a with those of module 21c are welded together as along line 43 (FIG. 2). Similarly the upper edge of module 21b and the lower edge of module 21e are welded together as along line 44 (FIG. 3). The interior stress bars or rods 24a are also welded to the flanges 23b of the adjoining modules 21c and 21c, as may be visualized in FIG. 7

The taper of module 21 conforms to that of module 21b so that a continuous taper of the Whole element 21a is obtained. The curvature of the module 2112 is such as to conform to the overall curvature of the dome.

Next in ring 33, a module 21 of the same length and taper as module 21e, by means of crane 36, is set into place with its lowermost end against and in registry with the uppermost part of module 21d and in between the projecting portions of modules 210 and 21g. The lower edge of module 21 is guided into place by the guide means 27 and 28 on module 21d (FIG. 6). While module 21 is held in place by the crane and the temporary scafiold, the adjoining flanges 23a of adjoining modules 21c and 21g are welded as along lines 45 and 46 (FIG. 2). The abutting lowermost edge of module 21f and uppermost edge of module 21d are also welded together.

Because alternate modules of the base ring 31 are of different lengths, the modules of ring 33 are interlocked with the modules of ring 31. The same interlocking will continue throughout the dome construction.

The stress bars 24a are welded interiorly of the module ring between flanges 23b of modules 210 and 21f and between modules 21 and 21g to complete the interior stress rings. The exterior stress bars 24 were added to the modules of ring 33 in the module forming process.

Additional modules are then similarly put into place and welded until the annular ring of modules 33 is completed. As described in connection with annular ring 31,

the stress bars or rods 24 and 24a form essentially complete rings for taking the tensile or compressive stresses developed and, being suflicient for this purpose in the completed structure, are suflicient to support the structure at this stage.

The next stage is to add, in like manner, a further annular ring of modules 47 and then further rings of modules, each ring of modules being of progressively smaller cross-section, until the apex is reached. The last ring of modules 34 includes alternate long and short modules in order to have even ends to the dome elements to which the compression ring 22 is Welded.

After the compression ring 22 has been attached, the structure is complete and any remaining temporary scaffolding may be removed.

Various dimensions of material and various materials may be used but one satisfactory material is ordinary hot rolled structural steel plate. Thus the panels 23 may be of structural steel plate one-quarter of an inch in thickness. Referring to FIG. 7, for a dome having a diameter of 1000 feet and a height at the center of 250 feet, the distance between flanges 23a of one module at the base of the dome may be sixteen feet, the vertical distance between the edges where flanges 23a and 23b join may be eight feet (i.e., the width of the panel at its widest is 11.31 feet). At the apex the modules have tapered uniformly to where the sixteen feet have become five feet and the eight feet have become thirty inches (panel width is 3.63 feet). The length of full length panels may be about sixty feet and the length of the short panels at the base and apex may be about thirty feet. The flanges 23a and 23b may be three-eights of an inch thick, seven inches wide throughout the distance along the dome surface from base to apex and of the same length as that of the panel. The flanges 23c and 23d may be three-eights of an inch thick and four inches wide throughout. The stitfeners may be one-quarter of an inch thick and four inches Wide on eachside throughout. The stress bars 24 and 24a may be ordinary steel pipe varying from six inch diameter pipe at the base of the dome, where the stress is the greatest, to lesser diameter pipes, for example one and one-half inch pipe, at the apex where stresses are less. Larger pipes than the one and one-half inch may be used at the apex if needed, for example up to the six inch pipe since the flanges are of appropriate dimensions. The pipes or stress bars may be spaced apart about twenty feet along the length of the modules.

In another embodiment of the present invention, shown in FIGS. 14-17, the manner of strengthening and rigidifying the modules comprises a number of longitudinal groeves 48 integrally associated with the tapered, longi tudinally and transversely curved panels 23. FIG. 16 shows three grooves or channels 48 having arcuate crosssections and spaced along the transverse width of the panel. It is obvious that a lesser or greater number of channels or grooves of varying shapes and spacings could be provided. The integral channels 48 which run from one longitudinal end of a panel 23 to the other, may be rolled into the panel surface. For additional edge stiffening the longitudinal edges may be bent over completely as at 49, As shown in FIG. 17, the transverse support rods 24 are attached to the modules, as by welding.

While welding has been described as a preferred form of joining the panels, the flanges to the panels and the stress bars to the flanges other methods may be used, such as bolts and nuts or rivets. Welding makes further sealing unnecessary and, as indicated makes, in effect, a monolithic structure. The panels are part of the supporting structure and form the cover or skin at the same time. The panels and stress bars together virtually, if not totally, eliminate the need for any separate supporting framework during construction.

While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover any such modifications as fall within the true spirit and scope of the invention.

The invention. having thus been described, what is claimed and desired to be secured by the Letters Patent 1. A dome building-construction resting on a support and having an apex, comprising a series of longitudinally arcuate, tapered, trough-like modules, having a generally V-shaped cross section, interconnected end-'to-end and side-by-side, said trough-like modules comprising two panels each of which is longitudinally and transversely curved, each of said two panels being tapered along its length and having, an interior edge, the interior edges of said two panels adjoining each other to form the said V-shaped cross section, the end-to-end connected modules being aligned in rows from said support to said apex and each row being continuously tapered along its length from a point of maximum width adjacent the support to a point of minimum width adjacent the apex.

2. The invention according to claim 1 wherein the apex of said dome includes a compression ring to which the uppermost ends of such dome surface elements are connected.

3. The invention according to claim 1 wherein the uppermost end of each module is equal in cross section to the lowermost end-of the module connected above it.

4. The invention according to claim 1 wherein trans= verse rods are connected at longitudinal intervals between the unjoined edges of each module having a generally V shaped cross section, and transverse rods are connected between the joined edge of each module and the joined edges of the module connected alongside thereof, the transverse rods of side-b'y-side modules being substantially aligned with each other to form stress bearing rings on the inner and outer surfaces of the dome.

5. The invention according to claim 1 wherein each panel includes aninner and outer flange along each longitudinal edge, said inner and outer flanges being in contiguous, angularly spaced relationship with each other, the flanges on opposite sides of each panel having the same angular relationship with respect to said panel but extending in opposite directions therefrom.

6. The invention according to claim 5 wherein transverse rods are connected at longitudinal intervals to the corresponding inner flanges of each of the panels.

7. The invention according to claim 6 wherein each of said longitudinally and transversely curved metal panels includes angular stiffening members attached to the surface thereof for substantially the full length of said panels.

8. The invention according to claim 6 wherein one end of one of said panels of each module includes guide members for receiving the other end of a corresponding panel of an adjacent modttle.

9. The invention according to claim 8 wherein the guide members comprise two arms of unequal length bent at the same angle but in different directions at a point the same distance from the end of the panel to which the guide members are attached.

10. A dome building construction module comprising in combination two longitudinally and transversely curved metal panels, each panel tapering in width from one end thereof to the other, said panels being assembled in edgeto-edge relation along one longitudinal edge thereof with the widest ends at one terminal edge of the module and the narrowest ends at the other terminal edge, means joining said panels in angular relation along said longitudinal edges to form a longitudinally arcuate tapered trough of V-shaped cross section, and bar means spanning said trough and being longitudinally spaced along the length thereof connecting the unjoined edges of said panels at longitudinal intervals.

11. The invention according to claim 10 wherein each panel includes flanges one each of which is attached to and contiguous with each of its longitudinal edges, said flanges, extending outwardly from the panel at the same angle but in opposite directions therefrom, the means for joining said panels is along adjoining flanges, and the bar means is attached to the flanges at the unjoined edges.

12. The invention according to claim 10 wherein each panel includes an inner and an outer flange along each longitudinal edge, said inner and outer flanges being in contiguous, angularly spaced relationship with each other, one edge of said inner flange being contiguous, along its full length, with the respective panel, the flanges 0n opposite sides of each panel having the same angular relationship with respect to the panel but extending in opposite directions therefrom.

13. The invention according to claim 12 wherein the means for joining said panels is along the adjoining inner flanges of adjacent panels, and the bar means are attached to the inner flanges at the unjoined edges of adjacent panels.

14. The invention according to claim 13 wherein each of said longitudinally and transversely curved panels includes angular stiffening members attached to the surfaces thereof for substantially the full length of said panels.

15. The invention according to claim 10 wherein each of said longitudinally and transversely curved panels includes stiffening portions comprising at least one integral bend along the full length of such panel.

References Cited UNITED STATES PATENTS 496,464 5/1893 White 52732 2,073,358 3/1937 Williamson 5282 2,231,396 2/1941 Smits 52-81 2,274,949 3/ 1942 Blaski 52-86 3,085,366 4/1963 Jamison 5281 3,154,889 11/1964 Monroe 52520 3,187,852 6/1965 Carman 52-86 FOREIGN PATENTS 480,273 1938 Great Britain.

HENRY C. SUTHERLAND, Primary Examiner US. Cl. X.R. 

